Fred; I seem to remember that not only were there some weight restrictions North of Durango, there was a clearance problem on one bridge which has since been replaced. I know that when they double headed the locomotives at some of the bridges they would stop and run the lead engine across
and then recouple after the other engine had
pulled the train across.
As for the tractive effort question, I believe I have heard that explanation before and since the
1938 Locomotive Cyclopedia shows the 488, a K-36,
as having 36,200 lb tractive effort it seems to fit.